1. Field of the Invention
The present invention relates to a D-jetronic control system that calculates a fuel injection amount based on intake pressure of an internal-combustion engine, and more particularly, to correcting a fuel injection amount in response to a change in intake pressure caused by inertia charge.
2. Description of the Related Art
A typical conventional internal-combustion engine control system (hereinafter referred to as an engine control system or ECU) determines the amount of fuel injected according to the engine speed of the internal-combustion engine and intake pressure. The ECU generally determines the fuel injection amount by referring to a two-dimensional map stored and retained in an internal read-only memory (ROM). The two-dimensional map provides correction coefficients of fuel injection amounts that are determined based on the engine speed and differential pressure.
FIG. 10 schematically illustrates the configuration of a conventional internal-combustion engine control system disclosed in Japanese Unexamined Patent Application Laid-open No. 9-287496.
As shown in FIG. 10, the engine is provided with an air cleaner 1, an intake manifold 2, a throttle valve 3, a throttle valve opening sensor 4, an intake pressure sensor 5, an injector 6, a spark plug 7, an exhaust manifold 8, a catalyst 9, an O.sub.2 sensor 10, a crankshaft 11, a crank angle sensor 12, a cam angle sensor 14, an exhaust cam pulley 15, an ECU 16, and a variable valve timing device actuator 17.
In the internal-combustion engine shown in FIG. 10, the ECU 16 determines the fuel injection amount based on engine speed, intake pressure, and amount of control of the variable valve timing device.
To be more specific, the ECU 16 determines the amount of fuel to be injected through the injector 6 according to the intake pressure detected by the intake pressure sensor 5, the engine speed detected by the crank angle sensor 12, a target value of valve timing advance (hereinafter referred to as "target advance") detected by phase difference between output signals of the crank angle sensor 12 and the cam angle sensor 14, and the control amount of the variable valve timing device 17.
During an intake stroke of the internal-combustion engine, a spark produced by the spark plug ignites the fuel-air mixture taken into a cylinder. The explosive power pushes a piston 21 down, and the torque of the crankshaft 11 is taken out of the internal-combustion engine.
At this time, the ECU 16 carries out feedback control according to the amount of remaining oxygen in the exhaust gas detected by the O.sub.2 sensor 10 so as to provide a stoichiometric ratio that permits the highest efficiency of exhaust gas purification in the catalyst 9.
Moreover, the ECU 16 also controls the control amount of the variable valve timing device 17 so that the target advance stored in the ROM agrees with the actual advance in valve timing (hereinafter referred to as "actual advance") detected by the crank angle sensor 12 and the cam angle sensor 14.
Generally, in an internal-combustion engine, under a condition wherein acceleration or deceleration is being performed at a given opening of a throttle valve (hereinafter referred to as a "transitional operation mode"), there are cases wherein the effect of inertia charge is more conspicuous than in a steady operation mode.
The inertia charge refers to a state wherein inertia of the flow of an intake air introduced into an engine causes more intake air to be pushed into the engine than in the steady operation mode even if the opening of the throttle valve remains constant.
More specifically, even if the opening of the throttle valve 3 remains constant, more intake air is pushed into the engine in the inertia charge mode than in the steady operation mode. For this reason, the intake pressure in the inertia charge mode is seemingly lower.
Therefore, the intake pressure in the transitional operation mode is sometimes lower than that in the steady operation mode.
The conventional internal-combustion ECU determines basic fuel injection amount based on intake pressure actually detected by intake pressure sensor 5. Therefore, the ECU decides that the amount of intaking air is decreased because the detected intake pressure is lowered under the transitional operation mode with the effect of inertia charge, and the fuel injection amount based on the detected intake pressure is decreased although the actual amount of intaking air is increased than that of steady state. As a result, sufficient amounts of fuel injection are not provided, and this has been posing problems such as air-fuel ratio (A/F ratio) fluctuations or feedback correction in the feedback control employing the O.sub.2 sensor 10 significantly changes.